I am fuzzy on whether the Apache handlers and processes are parent/child, siblings, single/same process, or something else. Perhaps the times function will do the job.

times Returns a four-element list giving the user and system times, in seconds, for this process and the children of this process.
( $user, $system, $cuser, $csystem ) = times;

This code shows that times does not wait until end-of-process or I/O operation to update its data source:

$ perl -wle 'sub r{@t=times();push @out,qq{@t}} sub x{my $z; $z.=1 for
+ 1..1_000_000;} r; x; r; x; r;print for @out'
0 0 0 0
0.17 0 0 0
0.29 0 0 0
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